The study compares the efficacy of methylphenidate, dextroamphetamine and placebo on neuropsychological functioning and behavioral symptoms in 36 children diagnosed with ADHD within a double-blind cross-over design over six weeks. The assessment of ADHD followed formalized guidelines and a diagnosis of ADHD was based on DSM-IV criteria. A neuropsychological testbattery and four behavioral questionnaires were selected as efficacy variables. The neuropsychological testbattery includes Qb-test (visual attention, inhibitory control, motor activity), Score (auditory attention), Stroop Test (processing speed, inhibitory control) and Grooved Pegboard (motor speed). The participants were tested once on each type of medication. The four questionnaires are: a)Side-Effects Rating Scale (completed by a parent at the end of each of the six weeks), b)Self-Report Questionnaire (completed by the child at the end of each of the six weeks), c)Parent and Teacher Questionnaire(completed by a parent and a teacher Monday till Friday through every week), Test Performance Questionnaire (completed by the child immediately after each of the three test sessions).